LED links needed!

[Anonymous]

I have a stupid question....


if you can wire 3 led's together in series and use a 12 volt power supply, why can't I wire 30 led's togeher in series and use a 120 volt power supply, All I need is a dohicky to make it DC instead of AC.....


Am I totally off base?

 

[minibowmatt]

you can.
But you will need to wire a big resistor at each LED to drop the voltage to the appropriate voltage. IMO, anyone who wires LED's in series without a resistor is looking for trouble anyway. it will work for a few months, but eventually they will burn out. If a surge gets in there, the resistor will stop it and keep your LED's lit. read through the links I posted earlier, they really teach you everything you need to know about wiring LED's

 

[Anonymous]

Will do...

 

[ShawnKM]

Here is a nice tool http://led.linear1.org/led.wiz and another led supplier http://www.superbrightleds.com/

 

[rfp]

In Costco this week and I saw a set of LED Icicle holiday lights for $4.95 that turned out to be 10 high intensity blue LEDs with a power supply. The product description is LED Icicle-Style Lights10 bulb from Kurt S. Adler.

The lights are wired in a 6 foot string with individual lights connected to a 1 foot wire off of the main string. The wall power supply plugs into a small controller module connected to the string. The controller cycles the light string from full on to off every few seconds.

With some minor modifications these lights can be used as aquarium moonlights. Each LED can be easily pried off the plastic icicle it is glued to. To modify the controller module to keep the LEDs on continuously, take apart the controller (2 screws) and remove the PCB (2 more screws), find the large resistor and unsolder the side connected opposite to the positive side of the power. Unsolder the positive side of the wire that exits the controller to the LED string and solder the resistor to it. This effectively bypasses the controller and directly connects the resistor to the LED string.

Looks great and you can't beat the price.

 

[Anonymous]

Welcome to RDO, and thanx for the info, rfp!

If anyone made the mod to the controller as described, please confirm it. Or post a circuit diagram and I will look it over.

 

[rfp]

The holiday lights didn't bring a schematic nor was I able to locate one, so I took the simple approach and bypassed the controller completely.

The resistor (20 Ohms) is connected to the drive transistor for the LEDs, the controller is connected to the base of the transistor (see attached iagram). The modification disconnects the drive transistor (at "X" in the diagram), and therefore all the controller circuitry, which results in the 20 OHM resistor being connected directly to 10 LEDs in parallel.

The source voltage measures 6.7V and the voltage drop across the led is 3.2 V making the current into all the LEDs equal to (6.7 - 3.2)/20= 175 milliamps. This should result in approximately 17.5 milliamps per LED, assuming equal current through each LED.

 

[Anonymous]

Looks like that will do the job. Thanx, rfp.